1. Field of the Invention
The present disclosure relates to an illumination apparatus and an image reading apparatus using the same. The concepts disclosed herein are particularly suitable for an image scanner, a copying machine, and a facsimile machine.
2. Description of the Related Art
An image reading apparatus, such as an image scanner, a copying machine, and a facsimile machine, line-sequentially reads an image while illuminating the target surface of a document. Conventionally, a document illumination apparatus used in such an image reading apparatus illuminates the target surface of a document using a tubular (linear) light source, such as a fluorescent light. Recently, since the light emission use efficiency of a light emitting diode (LED) has been improved, an illumination apparatus that uses a plurality of LEDs instead of a linear light source has been developed.
When using a nearly point-shaped light source such as an LED, a plurality of LEDs is arranged in a main scanning direction (a longitudinal direction of a document) to optimize the light amount distribution and the light amount itself in the main scanning direction. Further, to efficiently guide light from the LEDs to a read area on a surface to be illuminated, a light guide that uses internal reflection and refraction is used.
In such a document illumination apparatus, it is necessary to accurately set the positional relationship between the maximum intensity direction in light emission angle of LEDs as a light source and an entrance surface of the light guide to improve the light use efficiency as much as possible. In U.S. Pat. No. 7,760,403, a substrate on which LEDs are mounted serves as a holding member that holds the LEDs and a light guider. Further, an area of the substrate, the area holding the light guide, is used as a reflection surface, thereby preventing the decrease in light use efficiency.
However, in U.S. Pat. No. 7,760,403, when the light guide is fixed onto a substrate with a fixing member such as a double-sided tape interposed therebetween, some of rays of light incident on an entrance surface of the light guide enter the fixing member. It is difficult to use a fixing member such as a double-sided tape as a reflection surface. Therefore, even if a white double-sided tape having a high reflectance is used, rays of light that have entered the fixing member are irregularly reflected, and the light use efficiency thereby decreases.